High-elongation-and-tenacity nylon tire yarn

ABSTRACT

ELONGATION OF HIGH TENACITY YARN IS INCREASED BY HEATING THE YARN TO A TEMPERATURE BETWEEN 180* AND 235*C., WHIE UNDER A TENSION BETWEEN 0.05 AND 0.35 GRAM PER DENIER, FOR A PERIOD OF 0.003 TO 0.15 SECOND.

Mtlvch 21, 1972 E. P. BRIGNAC ETAL 3,651,201

HIGH-ELONGATION-AND-TENACITY NYLON TIRE YARN v Filed Aug. 21, 1968INVENTORS E. P. BRIGNAC B. E; SMITH E. J. SOLO WW SMITH United StatesPatent Oflice 3,651,201 Patented Mar. 21, 1972 3,651,201HIGH-ELONGATION-AND-TENACITY NYLON TIRE YARN US. Cl. 264-290 1 ClaimABSTRACT OF THE DISCLOSURE Elongation of high tenacity yarn is increasedby heating the yarn to a temperature between 180 and 235 C., while undera tension between 0.05 and 0.35 gram per denier, for a period of 0.003to 0.15 second.

The invention relates to a high tenacity yarn having a high elongation,and to a process for making such yarn. The yarn is particularly suitablefor use in tire construction.

Present known polyamide tire yarns have tenacities of approximately8.8-9.3 grams per denier and elongations of about l2.1-17.3%, the highertenacities corresponding generally to lower elongations. A minimumacceptable tenacity is about 8.5 grams per denier. Somewhat highertenacities can be produced by increasing the draw ratio, but this is atthe expense of a corresponding decrease in elongation in the usualprocess. Tire makers ply-twist the yarn to make tire cord, and then hotstretch or tensilize" the cord. A high elongation is desirable since itrenders the yarn and tire cord more resistant to impact breaks, as wellas atfording more eflicient use of the expensive hot stretchingapparatus.

Elongation of a drawn yarn is a measure of the degree to which the yarncan be stretched before it breaks, and is the length by which the yarncan be stretched divided by the original drawn length of the yarn. Thus,if a yarn of unit length can be stretched to a length of 1.20 unitsbefore breaking, the elongation is 0.20.

Merely increasing either tenacity or elongation, while suffering acorresponding decrease in the other, does not materially improve theyarn: both properties should have high values. A more useful indicationof yarn desirability than either of these properties considered alone istheir product. Thus, in a yarn having a tenacity of 9.3 grams and anelongation of 0.17, the product would be 1.58. Substantially improvedproperties are achieved when the tenacity-elongation product is at least1.65, and preferably at least 1.70, provided that the tenacity is atleast 8.5 grams per denier.

Applicants have discovered that elongation can be substantiallyincreased by subjecting the yarn to a specified temperature range whilethe yarn is under certain tensions, for specified time lengths, as ismore fully disclosed below, and that this increased elongation can beattained with little if any loss in tenacity.

Accordingly a primary object of the invention is to provide a hightenacity yarn having unusually high elongation.

A further object is to provide a yarn of the above character wherein theproduct of tenacity and elongation values are greater than 1.65, wherebyimproved yarn properties are achieved.

A further object is to provide processes for producing yarns of theabove character.

For a more complete understanding of the nature and objects of theinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawing, wherein the figure isa simplified perspective view of exemplary yarn drawing apparatusincorporating the invention.

Referring generally to the figure, undrawn yarn 20 is fed to drawingapparatus 22 which draws the yarn and orients the molecules therein. Thedrawn yarn is next passed over and in thermal contact with a heatedelement illustrated as plate 24 to increase its elongation, and then iscollected in an orderly fashion by means llustrated as a conventionaltwister takeup mechanism 26 including the usual ring and traveller.

Referring more specifically to the figure, nip rolls 28 feed yarn 20 ata predetermined rate. Yarn 20 next passes in one or more wraps aboutfixed draw pin 30 and across a fixed heater block 32 positioned belowdraw pin 30 in the zone of high tension between draw pin 30 and drawroll 34. Yarn 20 slides across the surface of plate 32 and then in aplurality of wraps about draw roll 34 and its associated freelyrotatable separator roll 36. The peripheral speed of draw roll 34 isselected to draw yarn 20 to a tenacity of at least 8.5 grams per denier.Drawing apparatus 22 as thus far specifically described is conventional.

According to the invention, yarn 20 next contacts hot plate 24 whileunder reduced tension. Yarn 20 next passes over guide roll 38 andthrough pigtail guide 40 to apparatus 26 where it is wound on bobbin 42.The size and temperature of plate 24 are selected in accordance with thespeed of yarn 20 so that yarn 20 is exposed to between 180 and 235 C.for a period between 0.003 and 0.15 second, while the yarn is under atension between 0.05 and 0.35 gram per denier.

As a specific example, the yarn was spun from polyhexamethyleneadipamide (nylon 66) polymer having a formic acid relative viscosity of73, as determined by A'STM method D-789-53T. Using the illustratedapparatu's, the relative speeds of nip rolls 28 and draw roll 34 wereselected to provide a draw ratio of 5.2 to 1 when roll 34 had aperipheral speed of 280 yards per minute. Block 32 was maintained at 190C., and was 1.5 inches long in the path contacted by the yarn. Ceramicpin 30 was 0.75 inch in diameter and was heated by yarn friction toabout C. Block 24 extended 6.5 inches along the yarn path, and wasmaintained at 210 C. The yarn tension while contacting block 24 was 0.14gram per denier, and was substantially the same as the tension be tweenroll 38 and pigtail guide 40.

Ring 44 was traversed back and forth parallel to the axis of bobbin 42between limits which converge as a function of time, as generallyillustrated in FIG. 9 of US. Pat. 2,764,363. Such a package constructionis called warp-wound, and is desirable in providing relatively uniformwind-on tension.

The tension on the yarn contacting block 24 can be maintained at a valuewithin the tension range specified above by selection of travellerweight and shape, and spindle r.p.m. If necessary, the spindle r.p.m.can be decreased as the bobbin diameter increases, to keep the tensionwithin the desired range. In this specific example, spindle r.p.m. islinearly decreased from 3150 r.p.m. at startup to 2700 r.p.m. at dofi,maintaining uniform tension of grams on the 840 drawn denier, filamentyarn.

Tenacity,

g.p.d. Elongation Product The yarns prepared according to the, presentprocess have substantially higher impact strength than do yarns such asthe control yarn having a tenacity-elongation product of less than about1.65, and permit more efficient use of the hot-stretching apparatus.Those yarns having a tenacity-elongation product greater than 1.70 areparticularly advantageous.

The terms tenacity and elongation as used in the specification andclaims refer to breaking tenacity and breaking elongation as determinedby ASTM test method D-2256, using a constant rate of elongation testingmachine as set forth therein.

Other drawing apparatus and string-ups can be used to provide the drawnyarn which is fed to hot plate 24. For example, the undrawn yarn can besupplied directly from the spinning apparatus, ,or can be wound beforebeing supplied to the drawing apparatus. The spun yarn separator rollcould be added between the takeu p mechanism 26 and plate 24, to isolatethe yarn contacting plate 24 from tension variations originating intakeup mechanism 26. The inertia of roll 38 performs this isolationfunction to a sufiicient extent in the illustrated preferred embodiment.We claim: 1. A process for producing high tenacity yarn having highelongation, said process comprising:

(a) drawing said yarn to a tenacity of at least 8.5

grams per denier, (b) reducing the tension on said yarn to a levelbetween 0.05 and 0.35 grams per denier, (c) subjecting said yarn whileat said reduced. tension level to a temperature between and 235 C. for aperiod between 0.003 and 0.15 second; and (d) collecting said yarn in anorderly fashion.

References Cited STANLEY N. GILREATH, Primary Examiner W. H. SCHROEDER,Assistant Examiner 1 US. Cl. X.R.'

28-713; 57157 S; 264-342 RE

